Phase I/II trial of adeno-associated virus-mediated alpha-glucosidase gene therapy to the diaphragm for chronic respiratory failure in Pompe disease: initial safety and ventilatory outcomes

Abstract

Pompe disease is an inherited neuromuscular disease caused by deficiency of lysosomal acid alpha-glucosidase (GAA) leading to glycogen accumulation in muscle and motoneurons. Cardiopulmonary failure in infancy leads to early mortality, and GAA enzyme replacement therapy (ERT) results in improved survival, reduction of cardiac hypertrophy, and developmental gains. However, many children have progressive ventilatory insufficiency and need additional support. Preclinical work shows that gene transfer restores phrenic neural activity and corrects ventilatory deficits. Here we present 180-day safety and ventilatory outcomes for five ventilator-dependent children in a phase I/II clinical trial of AAV-mediated GAA gene therapy (rAAV1-hGAA) following intradiaphragmatic delivery. We assessed whether rAAV1-hGAA results in acceptable safety outcomes and detectable functional changes, using general safety measures, immunological studies, and pulmonary functional testing. All subjects required chronic, full-time mechanical ventilation because of respiratory failure that was unresponsive to both ERT and preoperative muscle-conditioning exercises. After receiving a dose of either 1×10(12) vg (n=3) or 5×10(12) vg (n=2) of rAAV1-hGAA, the subjects' unassisted tidal volume was significantly larger (median [interquartile range] 28.8% increase [15.2-35.2], p<0.05). Further, most patients tolerated appreciably longer periods of unassisted breathing (425% increase [103-851], p=0.08). Gene transfer did not improve maximal inspiratory pressure. Expected levels of circulating antibodies and no T-cell-mediated immune responses to the vector (capsids) were observed. One subject demonstrated a slight increase in anti-GAA antibody that was not considered clinically significant. These results indicate that rAAV1-hGAA was safe and may lead to modest improvements in volitional ventilatory performance measures. Evaluation of the next five patients will determine whether earlier intervention can further enhance the functional benefit.

FIG. 1.

Schematic of the clinical trial timeline shows periodic safety and ventilatory testing before and up to 365 days after gene transfer. Throughout the study, patients received enzyme replacement therapy (ERT) and inspiratory muscle strength training (IMST) exercises.

FIG. 2.

Ventilatory function of subjects at study enrollment. (A) Although all subjects required full-time invasive ventilation, baseline maximal inspiratory pressure (MIP) varied appreciably between children. MIP values were >60% reduced from expected age- and sex-matched unaffected children. Solid and dashed lines represent average and upper/lower limits of age-predicted normal values for MIP. (B) Maximal voluntary ventilation (MVV) is influenced not only by respiratory muscle strength, but also by pulmonary mechanics, upper airway patency, and chest wall restrictive disease. MVV of the subjects was reduced >80% from healthy references. Unfilled bars represent the age, sex, and height-predicted reference value for each child. (C) The maximal-effort, unassisted tidal volumes of subjects fell short of the expected range of resting tidal volume in unaffected individuals (dashed lines).

FIG. 3.

Acute ventilatory function during the preoperative and 14-day postoperative periods. To date, five children have completed study procedures through the 180-day postoperative assessment. (A) During the preoperative period between the screening and baseline tests, subjects underwent preoperative inspiratory muscle strength training (IMST). Exercise alone did not acutely change the maximal inspiratory pressure (MIP) or the best-effort, unassisted tidal volume (VT). (B) Further, acute changes were minimal between the baseline tests performed the day before gene transfer and the day 14 postoperative test session (median [interquartile range]).

FIG. 4.

Presence of vector DNA and immune responses. (A) Quantitative real-time polymerase chain reaction was performed to assess the biodistribution of vector DNA in peripheral blood at baseline and days 1, 3, 14, 30, 60, 90, and 365 after administration. Serum samples were assayed by ELISA for circulating antibodies to the AAV1 capsid proteins (B) and intact human acid alpha-glucosidase (GAA) (C) at baseline and days 14, 30, 60, 90, 180, 270, and 365. Antigen-specific response assays challenged PBMCs with either vector (D) or intact transgene (E) product at baseline and days 14 and 90.

FIG. 5.

Ventilatory muscle function, following the gene transfer procedure. Patient performance was expressed in relation to the baseline function (dotted line at 100% reflects baseline function), measured the day before gene transfer. (A) The maximal unassisted tidal volume was significantly increased by day 180 (*p<0.05). No appreciable change was detected in (B) maximal voluntary ventilation or maximal inspiratory pressure (C). Although most patients achieved large relative gains in spontaneous ventilatory endurance (D), they did not reach statistical significance (p=0.08).